The invention relates to a system and method for determining degradation of an exhaust gas sensor downstream of an exhaust catalyst in an engine.
To meet current emission regulations, automotive vehicles must regulate the air-fuel ratio supplied to the vehicles"" engine cylinders to achieve maximum efficiency of exhaust gas catalysts. For this purpose, it is known to control the air-fuel ratio of internal combustion engines using an exhaust gas oxygen sensor positioned in the exhaust stream from the engine. The exhaust gas sensor provides feedback data to an electronic controller that calculates desired air-fuel ratio values over time to achieve optimum efficiency of a catalyst in the exhaust system. It is also known to have a system with two exhaust gas sensors in the exhaust stream in an effort to achieve more precise air-fuel ratio control with respect to a catalyst operational window. Normally, a pre-catalyst exhaust gas oxygen sensor is positioned upstream of the catalyst and a post-catalyst exhaust gas oxygen sensor is positioned downstream of the catalyst.
In connection with an engine having two groups of cylinders, it is known to have a two-bank exhaust system coupled thereto where each exhaust bank has a catalyst as well as pre-catalyst and post-catalyst exhaust gas sensors. Each of the exhaust banks corresponds to a group of cylinders in the engine. The feedback signal received from the exhaust gas sensors are used to calculate the desired air-fuel values in their respective group of cylinders at any given time.
Known engine control systems have also implemented strategies for determining when a pre-catalyst exhaust gas sensor becomes degraded. However, known engine control systems assume that post-catalyst exhaust gas sensors do not degrade since the sensors are buffered from a majority of the exhaust gases by the upstream catalyst. Thus, when a post-catalyst exhaust gas sensor does become degraded, an engine control system using a degraded output signal from the post-catalyst exhaust gas sensor will be unable to maintain optimal air-fuel values for optimal catalyst efficiency. Thus, the degraded post-catalyst exhaust gas sensor may result in increased emissions and decreased fuel economy.
The inventors herein have therefore recognized that there is a need for a system and method that determines when a post-catalyst sensor becomes degraded.
The foregoing problems and disadvantages are overcome by a system and method for determining degradation of a post-catalyst exhaust gas sensor in an engine in accordance with the present invention.
A method for determining degradation of a first exhaust gas sensor in an engine is provided. The engine is coupled to one or more exhaust gas catalysts for decreasing emissions. The method includes generating a first signal from a first exhaust gas sensor disposed downstream of a first catalyst. The method further includes determining an amount of oxygen supplied to one of the catalysts. Finally, the method includes determining degradation of the first exhaust gas sensor based on the amount of supplied oxygen and the first signal.
A system for determining degradation of a post-catalyst exhaust gas sensor utilized in an engine is also provided. The engine includes first and second cylinder banks coupled to first and second catalysts, respectively. The system includes a first exhaust gas sensor coupled downstream of the first catalyst generating a first signal. The system further includes a controller operably coupled to the first exhaust gas sensor. The controller is configured to determine an amount of oxygen supplied to one of the first and second catalysts. The controller is further configured to determine degradation of the first exhaust gas sensor based on the amount of supplied oxygen and said first signal.
Thus, the inventive system and method can determine when a post-catalyst exhaust gas sensor becomes degraded.